Grinding oil composition



Patented Nov. 16, 1948 GRINDING OIL COMPOSITION Everett C. Hughes, Cleveland Heights, and Franklin Veatch, Cleveland, Ohio, asslgnors to The Standard Oil Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application October, 15, 1946, Serial'No. 703,288

2 Claims. (Cl. 196-151) This invention relates to grinding oils, more particularly to an improved grinding oil composition which greatly increases the efiiciency of grinding operations.

Grinding oils are used when grinding metals, such as steel, with an abrasive grinding wheel. If the metal gets too hot during such a grinding operation with a worn wheel, the metal becomes discolored. The color may or may not indicate a deterioration in the quality of the metal, but it is undesirable commercially. After the wheel has been used to an extent where-the so-called temper color shows in the metal, it is necessary to redress the grinding wheel, 1. e., to resurface it by running a diamond point over the wheel surface to even out rough and worn spots.

The prior art commercial grinding oils do not allow the use of a grinding wheel to an extent where the surface of the wheel is so rough that it is no longer useful for precision grinding. Long before this point is reached, the wheel will have caused the metal to become discolored. In order to maintain the appearance of the finished piece the wheel must be resurfaced long before. its otherwise useful life is expended. It is customary. therefore, to appraise grinding oil in terms of the amount of grinding that can be done with a' wheel before it must be redressed.

It has been found, in accordance with the invention, that the efficiency of grinding operations may be considerably increased by the use of a new grinding oil composition, so that considerably more grinding can be done before redressing the grinding tool. The oil of this invention, moreover, delays the temper color formation sufficiently to allow grinding to proceed to a point where the wheel approaches more nearly its limit of usefulness as far as its surface is concerned. This oil, therefore, allows grinding to a point of greater deterioration of the wheel, because it helps prolong the use of the wheel before formation of temper color and need for redressing.

Grinding oils are to be distinguished from cut- ,ting oils and other lubricating oils such as are used in an internal combustion engine. Oils that are suitable for grinding may not be suitable for use in an internal combustion engine. Some oils which are good for cutting purposes are not good for grinding and vice versa. A cutting oil is generally used in cutting steel or other metal with a cutting tool. such as in a lathe, whereas a grinding oil'is used in grinding tempered steel with an abrasive. The grindability of tool steel is extremely sensitive to the type of grinding oil used, particularly under severe conditions of operation.

The objects achieved by the invention include the provision of new grinding oil compositions by the use of which a great increase in grinding efficiency is obtained, and other objects which will become apparent as the invention is described hereinafter.

It has been found, unexpectedly, that a composition comprising a mixture of two oils of widely divergent viscositles, gives much superior results when used as a grinding oil. One of the oils is a so-called "light" oil and has a relatively low viscosity or boiling point. If measured in viscosity it should be not over SUS at 100 F. and may be, for example, a straw oil having a viscosity of 50 to 100 SUS at 100 F. It should boil above 500 F. at atmospheric pressure so as not to flash during the grinding. The other oil has a very high viscosity in the range of 2000 to 6000 SUS at 100 F. This heavier oil may be, for example, a so-called bright stock and the following are given as examples with the viscosities (SUS) at 100 F. and 210 F. Generally the viscosity is measured at 210 F. and that at 100 F. calculated in a manner well known in the art:

SUSat210F 113 160 156 SUS at 100F 3740 4300 2100 3500 2218 These heavy viscosity oils are also characterized by their high boiling points.

The oil mixture should comprise from about 53 to 78 weight percent of the low viscosity oil and from about 47 to 22 weight percent of the high viscosity oil. These proportions are subject to the further qualification'that they be selected within the above ranges so that the mixture of oil should have a. viscosity in the range of 150 to 300 SUS at100 F., in order that the oil may flow properly as it is fed to the wheel during grinding.

The oils used are naturally occurring, um-efined mineral oil stocks.

By naturally occurring" stocks we mean oils which can be separated from naturally occurring mineral oils, such as petroleum, by distillation. They are to be distinguished from synthetic polymers, for example, such as hydrogenated polyisobutylene, polypropylene, or polypentene polymers which are prepared to have special properties for use in lubricating internal combustion engines.

Reference to the oils as being unreflned" refers to the oils as they are separated from the petroleum stock prior to any chemical or physical treatment to refine or finish them. They are to be distinguished therefore from oils which have 7 ing our grinding oils since they are much cheaper and are entirely satisfactory for this purpose. Such unrefined stocks would be unsuitable for lubrlcating oils for use in aircraft, automotive, high speed Diesel engines, and other lubricating uses requiring highly refined or finished oils.

In order to evaluate the efficiency of a grinding oil, a test was developed in which a commercial shop grinder was mounted with a dynamometer so as to measure the horizontal component of the grinding force as the steel is moved in contact with the grinding wheel. The grinding wheel speed, the speed of table'traverse of the steel against the wheel, and the rate of oil application are constant. The horizontal component of force measured in this test is an indication of the grinding efflciency, which is in turn related to the practical operating considerations such as wheel life, number of cuts made before wheel dressing, amount of heat generated during operation, permissible cutting speeds, etc.

In grinding tests on steel grinding out a section 10" in length and 0.040" deep, the following results were obtained with different unfinished oils:

Weight Per Weight Per Weight Per sea r Me m g eavy l E 111111 7a sue 4300 we 200 we gfigst 23 mm at 100 F. at 100 F. at 100 F.

100 None None 75 4, 300 05 35 None 210 3,380

None 100 None 7 4.300 None None 100 200 3, 700

oiitoovisconstobeusedasgrindingoii.

The mixture of light and heavy oils shows a'lower force component than any of the others, and may be viewed merely as illustrative of one of the preferred embodiments of the invention. Other tests indicate the range of proportions and viscosities suitable as described heretofore as comprising commercial grinding oils available on the open.

market, is illustrated by the following tests. These tests were made by grinding twist drills of the same size with automatic machines under identical conditions. A grinding oil composition was made up in accordance with the invention and consisted of 65 weight per cent of unrefined straw paraffin oil having a viscosity of 75 SUS at 100 F. and 85 weight per cent of unrefined bright stock having a viscosity of 4300 SUS at 100 F.; the viscosity of the grinding oil composition was 210 SUS at 100 F. The following results are typical:

The above oil mixture should comprise at least of the grinding oil composition, since the presence of about 10% of other oils or oil-like components does not interfere with the beneficial results from a composition, the major portion of which is made in accordance with the invention. Other ingredients may be present, such as detergents, alkali neutralized sulfonate hydrocarbons, such as the residue obtained from acid treated lubricating oil fractions, other lubricants such as fatty oils, lecithin, etc.

Although the invention is not limited to any particular theory, it is thought that the following comments may be of aid in understanding the operation of the oil.

Oils having ordinary vlscosities in the range of 175-275 SUS at F., which might becompared with the mixture of oils made in accordance with the invention, have a limited effectiveness because they are too light in bodyto lubricate effectively under the intense conditions encountered in grinding. I

The heavy oil in our composition is believed to be the active lubricant which lubricates the abrasive and steel surfaces because a major or substantial portion has a boiling point higher than that of the grinding temperature, and it is not vplatilized by the intense heat developed during the grinding. The heavy oil itself, however, is too viscous to flow into the very fine space between the abrasive and the metal. Therefore, if a heavy oil alone were used, there will be a failure of lubrication at the pointswhere it is needed most.

The light oil alone would not be a very eflicient lubricant, and furthermore, it is sufficiently volatile so that it flashes of]! to a certain extent at the very point where the abrasive touches the metal, due to the heat generated in the grinding operation. However, the light oil is light enough to flow into the fine space between the two surfaces.

In the mixture the light oil carries the heavy lubricating oil into the spaceto perform its lubricating function. The vaporization of the light oil is not suflicient to cause any appreciable thickening of the grinding oil. The oil is recycled in the grinding operation. losses being replenished by the 1. A grinding oil composition at least 90 weight per cent of which is composed of a mixture of an amount of an unrefined naturally occurring mineral oil having a viscosity of not over 100 SUS at 100 F. within the range of 53 to '78 weight per cent and an amount of an unrefined naturally scouring mineral oil having a viscosity of 2000 to 6000 SUS at 100 F. within the range of 47 to 22 weight per cent to provide a mixture having a guano viscosity in the range of 150 to 300 BUS at 100' l".

2. A grinding \oil composition at least 90 weight per cent or which is composed of a mixture of about 65 weight per cent 01 unrefined naturally occurring mineral oil at 100 F. and about 35 weight per cent of an unrefined naturally occurringmineral oil of viscosity of about 4300 SUS at 100 which mixture has a viscosity 01' about 210 SUB at 100 1''.

C. HUGHES.

FRANKLIN VEATCH.

of viscosity of about 75 SUS 6 REFERENCES crrnn UNITED sums PATENTS Number Name I Date 2,077,762 Lauer Apr. 20, 1937 2,183,783 Bray Dec. 19, 1939 l. 

